Head-worn optical instruments and devices such as glasses and sunglasses (i.e., eyewear) that incorporate electronic devices are generally known in the art. Examples of such devices include head-mounted displays (HMDs), also known as helmet mounted displays, which are worn on a head of a user and include an image source such as an electronic display that produces an image intended for being directed toward one eye (in the monocular case) or both eyes (in the binocular case) of that user. Another type of a head-worn device is an optical head-mounted display (OHMD), which is a see-through HMD (also known as an “optical see-though HMD”) that allows the user to both view through it, as well as to view generated images on it.
An example prior art device is disclosed in U.S. Patent Application Publication No.: US 2013/0044042 A1 to Olsson et al., assigned to Google Inc., entitled “Wearable Device with Input and Output Structures”, and directed at a head-mounted device for receiving user input and presenting information on its display. The head-mounted device includes a frame, two lens elements, a transparent display, an on-board computing system, a first projector, a second projector, a video camera, a sensor, and a finger-operable touch pad. The frame includes a center frame support, a plurality of lens elements, a center frame support, extending side arms. The extending side arms are configured to secure the head-mounted device to a face, nose, and ears of a user. The on-board computing system, the video camera, the sensor and the finger-operable touch pad are generally positioned on one of the extending side arms. The video camera is configured to capture images. The sensor includes a gyroscope or an accelerometer. The finger-operable touch pad receives user input by sensing finger movements of the user. The first projector is coupled to an inside surface of one of the extending side-arms and configured to project a display onto an inside surface of one of the lens elements. Similarly, the second projector is coupled to an inside surface of the other extending side-arms and configured to project onto an inside surface of the other lens elements. The lens elements act as combiners. Other embodiments include a single lens element that is coupled to one of the extending side arms or the center frame support. The single lens element includes a display that overlays computer-generated graphics upon the user's view. The on-board computing system is configured to receive and to analyze data from the video camera and the finger-operable touch pad and to generate images for output by the lens elements.